Flow cytometry devices are commonly employed to measure physical and/or chemical properties of particles such as cells (or other material) that are suspended in a fluid stream. Such information can be of significant value in a variety of circumstances. For example, doctors can utilize information derived using flow cytometry devices to obtain information regarding their patients' blood counts, white blood cell counts, leukemia progression and other characteristics. Also for example, flow cytometry devices can be used to conduct biological research, and for a variety of other purposes. A long standing commercial objective has been to reduce the complexity and cost of flow cytometry systems in order to make them more attractive for certain routine clinical diagnostic applications, such as HIV AIDS diagnosis and therapy monitoring. One pressing need for simpler, low-cost systems exists in Africa and Asia, where significant funds from organizations such as the WHO and the Gates Foundation are now available for the purchase of therapeutic drugs, but the availability of these expensive drugs is limited and the drugs are rationed based upon strict WHO diagnostic criteria that involve measurement of the patient's lymphocyte sub-populations (primarily CD4/CD8 counts and ratios).
Flow cytometry devices operate by shining light that is well-collimated (sometimes but not necessarily from a laser) onto a fluid passage through which is flowing a fluid carrying the cells (or other particles or material) of interest. Upon encountering the cells the light is scattered or absorbed. Depending upon the amount (and directions) of scattering and on the amount and color of the induced fluorescence, information can be determined about the characteristics of the cells. In addition, in many benchtop flow cytometry systems, dichroic mirrors are employed for separating fluorescence signals by wavelength. Optical filters are additionally used in such systems for selectively passing a particular wavelength band of interest to a detector. Typically, such systems employing dichroics and optical filters are bulky systems having multiple parts, which increase the complexity and cost of such cytometry systems. Thus, while at this time there remains a great need for information that can be reliably obtained through flow cytometry techniques, the relatively high complexity and costs of conventional flow cytometry techniques limit their use largely to laboratories within major metropolitan areas.
While many conventional flow cytometry systems are generally large, complicated and expensive devices insofar as the systems typically employ lasers, specialized lenses, expensive (e.g., quartz) glass flow tubes, and multiple photomultiplier tubes (PMTs), some attempts have also been made to develop smaller, less complicated, and less expensive systems. One type of system employs a transparent microfluidic channel through which flow the cells (or other particles or material) of interest, and polymer waveguides or fiber optics arranged along sides of the channel that are capable of directing light to, or conducting light away from, the channel. In at least some such systems, lenses are employed between the waveguides and the sides of the microfluidic channels so as to focus light directed toward the microfluidic channels.
Although such systems employing microfluidic channels and waveguides are potentially smaller and less expensive than many other types of conventional systems, systems of this type have certain disadvantages. In particular, because of the relative sizes of the waveguides, microfluidic channels and/or lenses in such systems, it is difficult to position multiple waveguides proximate a given microfluidic channel in such a way as to gather light emanating from the channel in different directions, such that it is difficult to gather multi-parameter data. Further, while the lenses are useful for guiding at least some of the light emanating from the channel, a significant amount of the light emanating from the channel nevertheless typically is lost as it passes over or under the waveguides. Also, it is often difficult to separate out or distinguish desired components of light emanating from a channel from other light components. Further, it is often difficult to control the positioning and speed of movement of sample materials of interest (e.g., cells, other biological materials, particulate matter) through the microfluidic channel and past one or more sensors in a manner that facilitates optical sensing of those materials of interest and results in the generation of useful optical data.
For at least these reasons, it would be advantageous if an improved system employing microfluidic channel(s), waveguide(s) and lens(es) could be developed that could be implemented as part of a microfluidic photonic sensor system for use in flow cytometry applications and/or other applications. It further would be advantageous if, in at least some embodiments, such an improved system allowed for better sensing of light emanating from a given microfluidic channel in a variety of directions, and/or was more efficient in directing light to the waveguides. It would additionally be advantageous if, in at least some embodiments, it was possible to separate out or distinguish among different portions of light of different spectra emanating from a microfluidic channel, without the complexity and cost associated with the use of dichroics, optical filters and the like. It would further be advantageous if, in at least some embodiments, it was possible to better control the positioning and movement of materials of interest within a sample for enhanced optical sampling.